The invention relates to polyester staple fibers or filaments with high resistance to pilling and a process for manufacturing them.
One of the most unpleasant phenomena brought about by the use of polyethylene terephthalate fibers in the textile industry, at first quite unexpected and confronting manufacturers of synthetic fibers with problems that are not even fully solved today, is pilling. Pilling is understood to mean the formation of small balls of fiber which arise on the textile by the fiber ends wandering out of the fabric structure and which are very detrimental to the appearance of the garments. The fibers holding the pills to the basic fabric do not break off because the polyester fibers have a far higher flexing abrasion resistance than the natural fibers so that the small balls of fiber or naps remain clinging to the fabric.
A known measure to counter pilling is the manufacture of polyesters with a low molecular weight or a low solution viscosity, which decreases the strength of the fiber to such an extent that the fiber ends and pills which have emerged break off rapidly as in the case of natural fibers. However, the reduction of about 40% in the fiber's strength makes it very susceptible to damage during the further processing of such fibers, so that this type of anti-pilling fiber can no longer be processed in the three-roller and rotor spinning mills at the same speeds and with the same efficiency as normal types of cotton.
From DE-OS 17 19 213, the process is known of admixing a combination of defined polyalkylene glycols and alkaline or alkaline earth salts of organic sulfonic acids to the polyethylene terephthalate after its polycondensation to deal with the problem of pilling. It is noted here that adding only polyalkylene ether of the type defined therein has practically no effect, but that serious faults occur during spinning and weaving processes.
To solve the problem of pilling, DE-OS 21 13 859 discloses the procedure of adding defined polyalkylene glycols to the initial components which form the polyester either before or after the transesterification reaction. Since these glycols are condensed into the polyester, a not inconsiderable number of the desired properties of the polyethylene terephthalate are altered, not to mention the fact that in this type of polyester it is sometimes very difficult to avoid producing an undesired three-dimensional structure.
To avoid the problem of pilling, JP-OS 54-120 732 suggests the admixture of 0.5 to 15% by weight, preferably 2-10% by weight, polyethylene glycol with a molecular weight of 300-4000 to the polyethylene terephthalate after its polycondensation. Studies have shown that the flexing abrasion resistance of fibers manufactured from this mixture is still far too high to produce a satisfactory pilling-resistant polyester fiber (see Comparative Example 2).